1. Field of the Invention
The present invention relates to a steering control system for use in a moving vehicle, and more particularly to a steering control system for use in a moving vehicle such as a moving automobile, an unmanned mobile and carrying device in a factory, or an automated vehicle for use in agriculture, civil engineering machinery and the like.
2. Description of the Prior Art
Heretofore, as a system for detecting a current position of a moving body such as the moving vehicles as described above, there has been proposed a system provided with a means for scanning a light beam emitted from a moving body in the circumferential direction or every azimuthal direction around the moving body, retroreflective means for reflecting the light beam in the direction of incident light which are secured at at least three reference positions apart from the moving body, and a beam receiver means for receiving light reflected by the retroreflective means (Japanese Patent Laid-open No. 67476/1984).
In the above mentioned prior art, differential azimuths between the adjoining two of three retroreflective means around the moving body, or included angles formed by the adjoining two of three retroreflective means with the moving body, are detected on the basis of the received beam output of the light-receiving means, and the position of the moving body is then calculated based on the detected differential azimuths and positional information of the retroreflective means or reference points which have been previously set.
In the above described system, however, there has been such a case where a light beam emitted from a beam source mounted on the moving vehicle could not be directed to the retroreflective means positioned at reference points because of an inclination or vibration of the moving vehicle, or a case where the light-receiving means on the moving vehicle receives light reflected from objects other than the expected retroreflective means.
When real reflected light is not positively received by a light-receiving means, the position of the moving vehicle is erroneously calculated so that the moving vehicle cannot be traveled along a prescribed course.
As a solution for the above-mentioned difficulties, the present applicant proposed a control system wherein on the basis of the azimuths of a light reflecting means as seen from the moving vehicle which were detected by the current and the last scans, the azimuth at which the same light reflecting means is to be detected in the next scan is predicted and the incident light from the predicted azimuth in the next scan is presumed to be the correct reflected light from the expected reflecting means (U.S. patent application Ser. No. 420,063, now U.S. Pat. No. 5,031,101 issued Jul. 9, 1991).
In the above control system, if no light signal is detected at the predicted azimuth, the predicted azimuth can be used for calculating the self-position of the moving vehicle as the azimuth at which the reflected light from the predetermined light reflecting means is detected, thereby to solve the problem due to a temporary missing of a light reflecting means, but the system for discriminating reference points or light reflecting means is easily complicated because it is required, for instance, to compare the detected azimuth and predicted azimuth of the light reflecting means for discriminating which light reflecting means the reflected light is coming from.